Figure 6
Red-shift of O-state absorption by Na+. Structure of KR2 (PDB:4XTL)16 on the left with close up on the proposed transient Na+ binding site close to D25115,31,49. At high [Na+] the presence of the charge (middle) caused a red-shift of the retinal absorption in the O state compared to the ground state, whereas the absorption was similar to the ground state absorbance in absence of Na+ (right). Scheme created using the dark state structure, no implications regarding the retinal isomerization state intended; helix2 is removed for visibility.
